The double particle には (niha/niwa) is just the target particle に (ni) combined with the topic particle は (ha/wa).
You can use this combination to make a time or location-related phrase the topic of the sentence.
| 冬には北海道に行きます。 ふゆ には ほっかいどう に いきます。 Fuyu ni ha (wa) Hokkaidou ni ikimasu. |
| As for when it’s winter (I) (will) go to Hokkaido. As for in-winter (I) (will) go to Hokkaido. In winter (I) (will) go to Hokkaido. |